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The metallic interstitial nitride Ni(3)N was prepared from Ni(NH(3))(6)Cl(2) and NaNH(2) in supercritical ammonia (p(NH(3)) approximately 2 kbar) at 523 K. Its previously reported crystal structure, as determined from X-ray powder data, was confirmed by neutron powder diffraction: Ni(3)N crystallizes in the hexagonal epsilon-Fe(3)N-type structure (P6(3)22, Z = 2, a = 4.6224 A and c = 4.3059 A at room temperature). The N atoms on the octahedral sites of an hcp arrangement of Ni show virtually complete occupational order at ambient temperatures, which is preserved up to its thermal decomposition at T approximately 600 K. This behavior is in marked contrast to that of the isotypic iron nitride, epsilon-Fe(3)N, which shows reversible partial disordering within the same range of temperatures. Possible reasons for the different behaviors of the two nitrides epsilon-Fe(3)N and Ni(3)N are discussed.

The crystal structures of the cotunnite-type phases (space group, Pnam, 2 = 4) of pure zirconia and hafnia prepared under high-temperature, high-pressure conditions in a multianvil device were refined by the-of-flight neutron powder Mraction. The structures of both compounds are very similar and the nine polyhedral metal-oxygen distances range from 2.133(1) to 2.546(1) di in Zr02 and from 2.121(1) to 2.535(2) di in Hf02. The Raman spectra of both phases resemble one another strongly and are consistent with the cotunnite-type structure. These results confirm that ZrOz and €NOz undergo transitions to the same phase at high pressure.

A powder sampie of 2MI muscovite, (Ko.90N3Qm)(A b .63Feo.23Mgo.l 6Tio.03)(SiJ.20Alo.80)OlO(OH)2, was studied by time-of-flight neutron diffraction at 1 bar and at 2(± 0.1) GPa. Rietveld refinements of the crystal structure were performed, varying all atomic coordinates in the room-pressure case (profile Rw = 0.013, Bragg intensities Rw = 0.040) and only the z coordinates of basal 0 atoms plus xyz of 0 and H of the OH group at 2 GPa (profile Rw = 0.035, Bragg intensities Rw = 0.181). In both cases the lattice constants were refined: a = 5.2108(4), b = 9.0399(8), c = 20.021(2) Ä, ß = 95.76(1)" (1 bar), a = 5.187(2), b = 8.995(4), c = 19.502(4) A, ß = 95.78(2)" (2 GPa). The unit-cell compression shows deviations from linear elastic behaviour. Inter-layer K-O bonds are compressed along z more than the c lattice constant. The O-H group forms an angle of 85(1)" with c • and establishes three very loose contacts (H .. O from 2.62 to 2.67 A) with neighbouring 0 atoms. This environment does not change appreciably at 2 GPa.